Color flat panel display sub-pixel rendering and driver configuration for sub-pixel arrangements with split sub-pixels

ABSTRACT

Various embodiments of a sub-pixel repeating group are disclosed. In one embodiment, an octal subpixel repeating group may comprise three-color (red, green and blue) sub-pixels with blue colored subpixel comprising twice the number of positions within the octal sub-pixel grouping as the red and green colored sub-pixels. In another embodiment, a subpixel repeating group comprises two rows of eight “split” subpixels comprising three primary colors and a non-saturated neutral, or white, subpixel functioning as a primary color.

RELATED APPLICATIONS

This application is a continuation in part of co-pending U.S. patentapplication Ser. No. 10/278,352 filed on Oct. 22, 2002, and claims thebenefit of priority thereof. This application is also a continuation inpart of co-pending U.S. patent application Ser. No. 10/821,353 filed onApr. 9, 2004, and claims the benefit of priority thereof. U.S. patentapplication Ser. No. 10/278,352 claims priority to U.S. ProvisionalPatent Application Ser. No. 60/346,738 (“the '738 provisionalapplication”), filed on Jan. 7, 2002, which is hereby incorporated byreference herein.

U.S. patent application Ser. No. 10/278,352 is published as U.S. PatentApplication Publication 2003/0128179, which is hereby incorporated byreference herein. U.S. patent application Ser. No. 10/821,353 ispublished as U.S. 2005/0225574, which is hereby incorporated byreference herein.

The present application is also related to commonly owned U.S. patentapplication Ser. No. 10/278,328, entitled “IMPROVEMENTS TO COLOR FLATPANEL DISPLAY SUB-PIXEL ARRANGEMENTS AND LAYOUTS WITH REDUCED BLUELUMINANCE WELL VISIBILITY,” filed on Oct. 22, 2002, published as U.S.Patent Application Publication 2003/0117423 (‘the '423 application”);U.S. patent application Ser. No. 10/278,393, entitled “COLOR DISPLAYHAVING HORIZONTAL SUB-PIXEL ARRANGEMENTS AND LAYOUTS,” filed on Oct. 22,2002, published as U.S. Patent Application Publication 2003/0090581 (the“581 application”); and U.S. patent application Ser. No. 10/278,353,entitled “IMPROVEMENTS TO COLOR FLAT PANEL DISPLAY SUB-PIXELARRANGEMENTS AND LAYOUTS FOR SUB-PIXEL RENDERING WITH INCREASEDMODULATION TRANSFER FUNCTION RESPONSE,” filed on Oct. 22, 2202,published as U.S. Patent Application Publication 2003/0128225. Publishedpatent applications U.S. 2003/0128179, U.S. 2003/0117423, U.S.2003/0090581 and U.S. 2003/0128225 are all hereby incorporated byreference herein.

BACKGROUND

The present application relates to improvements to display subpixellayouts, and, more particularly, to improved color subpixelarrangements, means of addressing used in displays, and to data formatconversion methods for these displays.

Full color perception is produced in the eye by three-color receptornerve cell types called cones. The three types are sensitive todifferent wavelengths of light: long, medium, and short (“red”, “green”,and “blue”, respectively). The relative density of the three differssignificantly from one another. There are slightly more red receptorsthan green receptors. There are very few blue receptors compared to redor green receptors.

The human vision system processes the information detected by the eye inseveral perceptual channels: luminance, chromanance, and motion. Motionis only important for flicker threshold to the imaging system designer.The luminance channel takes the input from only the red and greenreceptors. In other words, the luminance channel is “color blind.” Itprocesses the information in such a manner that the contrast of edges isenhanced. The chromanance channel does not have edge contrastenhancement. Since the luminance channel uses and enhances every red andgreen receptor, the resolution of the luminance channel is several timeshigher than the chromanance channels. Consequently, the blue receptorcontribution to luminance perception is negligible. The luminancechannel thus acts as a resolution band pass filter. Its peak response isat 35 cycles per degree (cycles/°). It limits the response at 0 cycles/°and at 50 cycles/° in the horizontal and vertical axis. This means thatthe luminance channel can only tell the relative brightness between twoareas within the field of view. It cannot tell the absolute brightness.Further, if any detail is finer than 50 cycles/°, it simply blendstogether. The limit in the horizontal axis is slightly higher than thevertical axis. The limit in the diagonal axes is significantly lower.

The chromanance channel is further subdivided into two sub-channels, toallow us to see full color. These channels are quite different from theluminance channel, acting as low pass filters. One can always tell whatcolor an object is, no matter how big it is in our field of view. Thered/green chromanance sub-channel resolution limit is at 8 cycles/°,while the yellow/blue chromanance sub-channel resolution limit is at 4cycles/°. Thus, the error introduced by lowering the red/greenresolution or the yellow/blue resolution by one octave will be barelynoticeable by the most perceptive viewer, if at all, as experiments atXerox and NASA, Ames Research Center (see, e.g., R. Martin, J. Gille, J.Larimer, Detectability of Reduced Blue Pixel Count in ProjectionDisplays, SID Digest 1993) have demonstrated.

The luminance channel determines image details by analyzing the spatialfrequency Fourier transform components. From signal theory, any givensignal can be represented as the summation of a series of sine waves ofvarying amplitude and frequency. The process of teasing out,mathematically, these sine-wave-components of a given signal is called aFourier Transform. The human vision system responds to thesesine-wave-components in the two-dimensional image signal.

Color perception is influenced by a process called “assimilation” or theVon Bezold color blending effect. This is what allows separate colorpixels (also known as sub-pixels or emitters) of a display to beperceived as a mixed color. This blending effect happens over a givenangular distance in the field of view. Because of the relatively scarceblue receptors, this blending happens over a greater angle for blue thanfor red or green. This distance is approximately 0.25° for blue, whilefor red or green it is approximately 0.12°. At a viewing distance oftwelve inches, 0.25° subtends 50 mils (1,270 μ) on a display. Thus, ifthe blue pixel pitch is less than half (625 μ) of this blending pitch,the colors will blend without loss of picture quality. This blendingeffect is directly related to the chromanance sub-channel resolutionlimits described above. Below the resolution limit, one sees separatecolors, above the resolution limit, one sees the combined color.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in, and constitute apart of this specification illustrate various implementations andembodiments.

FIG. 1 shows an arrangement of sub-pixel emitters comprising threescolors—red, green, and blue—in groupings that create a largerrectilinearly repeating cell group of eight sub-pixels wherein the bluesub-pixels are “split”.

FIGS. 2, 3 and 4 illustrate one embodiment of red, green, and blueresample area arrays for the red, green and blue color planesrespectively to match the sub-pixel arrangement of FIG. 1.

FIGS. 5 and 6 illustrate the red and green resample area arrays of FIGS.2 and 3 overlaid on the sub-pixel arrangement of FIG. 1 respectively.

FIG. 7 illustrates one particular inter-color-plane-phase relationshipbetween the red and green color resample areas overlaid on the sub-pixelarrangement of FIG. 1.

FIGS. 8A and 8B illustrate two possible schematics for a driverarrangement for the arrangement of color emitter sub-pixels in FIG. 1.

FIGS. 9 and 10 show two “dot inversion” schemes—commonly known as “2×1”and “1×1”, respectively—matching FIG. 8A's schematic.

FIGS. 11 and 13 depict alternative blue color plane resample area arraysto replace the one shown in FIG. 4.

FIGS. 12 and 14 show how the respective blue color plane resample areasof FIGS. 11 and 13 would map onto the sub-pixel layout as shown in FIG.1.

FIGS. 15 and 16 show two “dot inversion” schemes—commonly known as “2×1”and “1×1”, respectively—matching FIG. 8B's schematic.

FIG. 17 illustrates the results of turning on two full color incomingdata pixels.

FIGS. 18A and 18B show other embodiments of the octal subpixelarrangement with various vertical displacements of the subpixels.

FIGS. 19A and 19B show yet other embodiments of the octal subpixelarrangement of various displacements of the split majority subpixelwithin the subpixel grouping.

FIG. 20 depicts a system incorporating sub-pixel rendering techniquessuitable to drive a panel made in accordance with the variousembodiments described herein.

FIG. 21 shows the arrangement of sub-pixels of FIG. 1, and illustratesthe concept of “splitting” the blue sub-pixels.

FIG. 22 illustrates a portion of a display panel comprising a subpixelrepeating group that includes subpixels in three primary colors and awhite subpixel that functions as a fourth primary color.

FIG. 23 illustrates a portion of another display panel comprising thesubpixel repeating group of FIG. 22 in which the subpixels are arrangedin a different color order.

FIG. 24 illustrates a portion of another display panel comprising thesame subpixel repeating group of FIG. 23 having a different aspectratio.

FIG. 25 is a schematic diagram of a portion of a liquid crystal displayand illustrating the use of an enlarged black matrix adjacent to colorfilters.

FIG. 26 illustrates the concept of splitting the subpixels in thesubpixel repeating group of FIG. 23 to produce a new subpixel repeatinggroup.

FIG. 27 illustrates a portion of a display panel comprising the subpixelrepeating group of FIG. 26 having the split sub-pixels.

FIG. 28 is a schematic diagram of a portion of a driver configurationfor the poriton of the display panel of FIG. 27.

FIG. 29 is a block diagram of a display device that includes a displaypanel comprising the subpixel repeating group of FIG. 26 with the splitsubpixels.

FIG. 30 is a schematic diagram of an enlarged portion of a TFT array forthe subpixel repeating group of FIG. 26, showing crossover connectionsbetween subpixel areas.

DETAILED DESCRIPTION

Reference will now be made in detail to various implementations andembodiments, examples of which are illustrated in the accompanyingdrawings. Wherever possible, the same reference numbers will be usedthroughout the drawings to refer to the same or like parts.

Display Panel Comprising Subpixel Repeating Group With “Split Blue”Subpixels

In FIG. 1, in the arrangement of sub-pixel emitters 100, there arethree-color emitters in groupings 120 that create a larger rectilinearlyrepeating cell group of eight sub-pixels. This layout was introduced inthe '738 provisional application and included herein by reference.Grouping 120 comprises red sub-pixels 104, green sub-pixels 106 and bluesub-pixels 102. As may be seen, blue sub-pixels 102 are “split”—i.e.having a smaller width along the horizontal axis than either red orgreen sub-pixels but doubled in number per grouping or repeat cell. Sucha “split” sub-pixel can refer to a sub-pixel having a smaller area thana non-split sub-pixel. Splitting the blue sub-pixels helps in breakingup the noticeable effect of visible vertical blue stripes down thedisplay, as further discussed in the related '423 application referencedabove.

As may additionally be seen in FIG. 1, the red and the green sub-pixelsare placed upon a “checkerboard” pattern with the repeat cell itself Asdiscussed further in related U.S. Patent Application Publication2003/0128225 referenced above, it may be desirable to alter the colorassignments in repeat cell grouping 120 to have a split green sub-pixelin position of sub-pixels 102 and have the remaining red and bluesub-pixels form the checkerboard pattern. Likewise, it might bedesirable to have the red sub-pixels split and the green and bluesub-pixels on a checkerboard pattern. The alternating “checkerboard” ofemitters is similar to the red and green “checkerboard” that wasdisclosed in commonly assigned U.S. patent application Ser. No.09/916,232, entitled “ARRANGEMENT OF COLOR PIXELS FOR FULL COLOR IMAGINGDEVICES WITH SIMPLIFIED ADDRESSING,” filed on Jul. 25, 2001, and nowissued as U.S. Pat. No. 6,903,754 (‘the '754 application”). U.S. Pat.No. 6,903,754 is hereby incorporated by reference herein.

It should be appreciate that while FIG. 1 depicts the “split” bluesubpixel as narrower than either the red or the green subpixels, anotherembodiment of the present invention employs blue subpixels of equal areadimensions to the red and green subpixels. To achieve a pleasing whitepoint with all subpixels on in a logical pixel, the relative intensities(luminance) of the red, green and blue emitters may be changedappropriately, as discussed in co-pending and commonly assigned U.S.patent application Ser. No. 10/243,094, entitled “IMPROVED FOUR COLORARRANGEMENTS OF EMITTERS FOR SUB-PIXEL RENDERING,” filed Sep. 13, 2002,and published as U.S. Patent Publication No. 2004/0051724. U.S. PatentPublication No. 2004/0051724 (“the '724 application”) is herebyincorporated by reference herein. For example, in the '724 application,several techniques are discussed for adjusting the red and greensubpixels to be of equal luminance. One embodiment comprises keeping thesame chromaticity points but increase the transmission of the lowerluminance filter. There are several ways to accomplish this result: (1)make the red filter physically thinner than the green filter; (2) changethe red pigment to either (a) reduce the amount of pigment in thefilter; or (b) apply a different pigment comprising the samechromaticity but allows for greater transmissivity of light; or (3)apply a red filter that maintains substantially the same center ofchromaticity but broadens the range of frequencies on either side of thecenter point.

Another embodiment would keep the same chromaticity point but decreasethe transmission of the higher luminance filter. As above, there areseveral ways to accomplish this result: (1) make the green filterphysically thicker than the red filter; (2) change the green pigment toeither (a) increase the amount of pigment; or (b) apply a differentpigment comprising the same chromaticity but allows for a lessertransmissivity of light; or (3) apply a green filter that maintainssubstantially the same center of chromaticity but narrows the range offrequencies passed through on either side of the center point.

Another embodiment may be to increase the energy from the backlight ofthe transmissive panel (e.g. LCD) in the pass band of the lowerluminance color filter relative to the higher luminance color filterpass band.

As shown in FIG. 1, the subpixels appear to have a substantiallyrectangular appearance. It should be appreciated that other shapes tothe subpixels are also possible and are contemplated within the scope ofthe present invention. For example, a multitude of other regular orirregular shapes for the subpixels are possible and are desirable ifmanufacturable. It suffices only that there is an octal grouping ofcolored subpixels in the fashion herein described that may beaddressable for the purposes of subpixel rendering (SPR).

As subpixel shapes may vary under the scope of the present invention, sotoo may the exact positions of the subpixels be varied under the scopeof the present invention. For example, FIGS. 18A and 18B depict asimilar octal subpixel grouping wherein one or both of the majoritystripes 102 are offset (relatively or otherwise) from the othersubpixels 104 and 106. Other vertical offsets are also possible.

Other embodiments of the octal groupings are also possible. FIGS. 19Aand 19B depict octal groupings wherein the majority subpixels 102 areinterspersed within the checkerboard of subpixels 104 and 106. Otherarrangements of majority subpixel placement within such a checkerboardare also possible and are contemplated within the scope of the presentinvention.

FIGS. 19A and 19B may have column electrodes that zig-zag across thedisplay. Column driver savings should be one third when compared to theRGB stripe system with the same resolution and the number of subpixelsare about two thirds of the number of subpixels when compared to the RGBstripe system.

Yet other embodiments of the present invention are possible. Forexample, the entire octal subpixel groupings may be rotated 90 degreesto reverse the roles of row and column driver connections to thegrouping. Such a horizontal arrangement for subpixels is furtherdisclosed in the related, co-pending and commonly assigned '581application referenced above.

Subpixel Rendering Techniques for Subpixel Repeating Groups With “SplitBlue” Subpixels

With the display comprised substantially of repeat cell 120 having theblue sub-pixel split as sub-pixel 102, it is possible to performsub-pixel rendering upon this display using the area resamplingtechniques as described in commonly-owned U.S. patent application Ser.No. 10/150,355, entitled “METHODS AND SYSTEMS FOR SUB-PIXEL RENDERINGWITH GAMMA ADJUSTMENT,” filed on May 17, 2002, and published as U.S.Patent Publication No. 2003/0103058 (“the '058 application”). U.S.Patent Publication No. 2003/0103058 is hereby incorporated by referenceherein. One such embodiment of area resampling is shown in FIGS. 2through 7.

FIGS. 2, 3 and 4 illustrate red 200, green 300, and blue 400 resamplearea arrays for the red, green and blue color planes, respectively. Itshould be noted that each color resample area array 200, 300, and 400comprises of resample areas 206, 306 and 404 and that each resample areahas an associated resample point 202, 302 and 402, respectively. Theresample points 202, 302, and 402 match the relative positions of thered 104, green 106 and blue 102 sub-pixel locations, respectively,within each color plane; but not necessarily their exactinter-color-plane-phase relationships. Any number of phase relationshipsare possible, a number of which have useful properties in given dataformat conversion cases.

FIGS. 5 and 6 illustrate the red and green resample area arrays of FIGS.2 and 3 overlaid on the sub-pixel arrangement 100 of FIG. 1,respectively. FIG. 7 illustrates one particular inter-color-plane-phaserelationship between the red and green color resample areas overlaid onthe sub-pixel arrangement 100. This particular inter-color-plane-phaserelationship depicts converting the conventional fully converged squaregrid red-green-blue RGB format which is to be displayed “one-to-one”with the square blue 102 sub-pixel grid. In this inter-color-plane-phaserelationship, the green 300, blue 400, and red 200 resample area arraysare positioned such that the red 202 and green 302 resample pointsoverlap the blue 402 sample points. This treats the blue sub-pixels 102as though they lay on top of, or intimately associated with, the red 104and green 106 sub-pixel checkerboard.

FIGS. 11 and 13 depict alternative blue color plane resample area arraysto replace the one shown in FIG. 4. FIGS. 12 and 14 show how theserespective blue color plane resample area would map onto the sub-pixellayout as shown in FIG. 1. FIGS. 11 and 13 depict two differentembodiments of resample areas 406 for blue with the phase shift shown.It should be appreciated that other phase shifts suffice for thepurposes of the present invention. Additionally, other resample areasfor the blue pixel data could be employed without departing from thescope of the present invention.

These Figures are merely illustrative and only serve to provide anunderstanding of the relationship between the resample points,reconstruction points, resample areas, and sub-pixel locations for thisembodiment.

The sub-pixel rendering techniques as described in the '058 patentapplication can be used to convert the incoming data format to thatsuitable for the display. In such a case, the method proceeds asfollows: (1) determining implied sample areas for each data point ofincoming three-color pixel data; (2) determining the resample area foreach color sub-pixel in the display; (3) forming a set of coefficientsfor each said resample area, the coefficients comprising fractions whosedenominators are a function of the resample area and the numerators area function of an area of each said implied sample areas that maypartially overlap the resample areas; (4) multiplying the incoming pixeldata for each implied sample area by the coefficient resulting in aproduct; (5) adding each product to obtain luminance values for eachresample area.

Other sub-pixel rendering techniques are possible to employ with thevarious sub-pixel arrangements as disclosed herein. For example, thetechniques known as “adaptive filtering” may be employed in the samefashion as described in U.S. Patent Application Publication No.2003/0085906 (‘the '906 application”) entitled “METHODS AND SYSTEMS FORSUB-PIXEL RENDERING WITH ADAPTIVE FILTERING,” filed on Aug. 8, 2002 asU.S. patent application Ser. No. 10/215,843 and is commonly owned by thesame assignee of this application. U.S. 2003/0085906 is herebyincorporated by reference herein. Adaptive filtering can be adopted soas not to require a 3×3 sample of input data, which uses a minimum oftwo lines of memory. The test may be based on a smaller sample of inputdata, for example 1×3 or 1×2 matrices. The input data is sampled to testfor vertical or diagonal lines, dots and edges, or other high contrastfeatures and then actions are taken, depending on the outcome of thetests.

Test masks may be used and compared to the image data to see if an edgeis detected; if detected then take an appropriate action to the redand/or blue data—e.g. apply gamma or apply a new value or differentfilter coefficient. Otherwise, if no feature is detected, then no actionmay be taken.

FIG. 17 illustrates the results of turning on two full color incomingdata pixels. The two pixels are converted to two clusters of sub-pixels,called “logical pixels”, turned on at varying amplitudes. The logicalpixel on the left is centered on or near a green sub-pixel 106. Thelogical pixel on the right is centered on or near a red sub-pixel 104.In both logical pixels, the various sub-pixels are turned on to theappropriate illumination such that a pleasing white color is formed andcentered on the green and red sub-pixels, respectively. Driveraddressing arrangements for display panels having subpixel repeatinggroups with “split blue” subpixels

FIGS. 8A and 8B illustrate two possible schematics for a driverarrangement 800 for the arrangement of color emitter sub-pixels inFIG. 1. FIG. 8A shows a one to one correspondence of column drivers tocolumns in the display; however, with the split blue sub-pixels, it maybe desirable to tie adjacent columns of split blue sub-pixels viaconnections 820. As may be seen in FIG. 8B, this scheme has theadvantage of saving on the number of column drivers.

For convenience, these examples given have the same number of sub-pixelsillustrated as FIG. 1. These drive arrangements may be used for a numberof display technologies, as the blocks 810 may represent one or severalelectrical components. They may represent the capacitive display cellelement for passively addressed Liquid Crystal Display (LCD), orElectroLuminescent (EL) Display. It may represent the gaseous dischargeelement in a Plasma Display Panel (PDP). It may represent thesemiconductor diode element of a passively Inorganic Light EmittingDiode or an Organic Light Emitting Diode Display. It may represent thetransistor, storage capacitor, and capacitive cell element of an ActiveMatrix Liquid Crystal Display (AMLCD). It may represent themulti-transistor, storage capacitor, and light emitting element of anActive Matrix Organic Light Emitting Diode Display (AMOLED). It mayrepresent, in general, the color sub-pixel and its associated electronicelements found in other known or yet to be invented displaytechnologies.

Known drive timing and methods may be used for N X M drive matrices asthose shown. However, there may be modifications needed due to thespecific color assignments, particularly any checkerboard across thepanel or color alternations within a single column. For example, thetechnique known in the art as Multi-Line Addressing for passive LCD maybe modified such that groupings of rows are restricted to odd and evenrow combinations. This will reduce potential color cross talk since,within a column with two alternating color sub-pixels, only one colorwill be addressed at a time.

Inversion schemes, switching the electrical field polarity across thedisplay cell to provide a time averaged zero net field and ion currentacross the cell can be used to the above unique sub-pixel arrangements.FIGS. 9 and 10 (matching FIG. 8A's schematic) and FIGS. 15 and 16(matching FIG. 8B's schematic) show two “dot inversion” schemes—referredto as “2×1” and “1×1”, respectively—on Active Matrix Liquid CrystalDisplays, both of which will perform satisfactorily. The scheme shown onFIGS. 9 and 15 may perform better when slight imbalances of lighttransmission occur between positive and negative polarities, especiallywhen the eye is tracking the motion of displayed images moving acrossthe screen. Each of the Figures shows the polarities during half of thedisplay addressing fields. The polarities are reversed for the otherhalf, alternating every field, resulting in a net zero current (zero DCbias), as is well known in the art.

FIG. 20 depicts a system 2000 in which a display as constructed inaccordance with the various embodiments disclosed herein is driven by asub-pixel rendering technique 2004 which may be resident on a physicaldevice 2002. An input image data stream 2008 may be input into thesub-pixel rendering technique 2004 and converted in the manner hereindisclosed. An output image data stream 2010 is sent to the displaydevice 2006 in order to drive the various sub-pixels to form an imagethereupon. As discussed in several references incorporated herein, thesub-pixel rendering (SPR) technique 2004 may be implemented in eitherhardware and/or software or a combination thereof For example, SPRtechniques 2004 could be resident as logic (either hardware or software)on the display itself or it could reside on a graphics controller chipor board.

Display Panels Comprising Additional Subpixel Repeating Groups With“Split” Subpixels

As noted in the related '423 application referenced above, in prior artRGB stripe display panels, the blue subpixels are seen as producingvisible stripes on the display. That is, when viewed, the luminancechannel of the human vision system sees blue subpixels as dark (black)stripes alternating with the combination of the red and green subpixels,which produces white stripes. In the horizontal direction, there arefaint, but discernable lines between rows of three-color pixel elementslargely due to the presence of the transistors, and/or associatedstructures, such as capacitors, at each subpixel, as is common in theart.

FIG. 21 illustrates subpixel repeating group 2100 showing a two-rowarrangement of six subpixels including two red subpixels 104 (shown withvertical hatching as in the figures above), two green subpixels 106(shown with diagonal hatching as in the figures above) and two bluesubpixels 102 (shown with horizontal hatching as in the figures above).Dividing, or “splitting” the single blue subpixel 102 in each row intotwo subpixels, each having a smaller width in the horizontal direction,and then inserting one of the smaller blue subpixels 102 between the redand green subpixels, produces subpixel repeating group 120 of FIG. 1herein. As noted above, the luminance channel of the human vision systemno longer sees visible stripes, but rather sees black dots alternatingwith white dots. This is an improvement because the spatial frequency,i.e. Fourier Transform wave component, and the energies of thesecomponents are now spread into every axis, vertical, diagonal, as wellas horizontal, reducing the amplitude of the original horizontal signal,and thus, the visual response (i.e., visibility).

In U.S. Patent Application Publication 2005/0225574 (“the '574application”), which is published U.S. patent application Ser. No.10/821,353, entitled “Novel Subpixel Layouts and Arrangements for HighBrightness Displays,” it is noted that an electronic display may bestrender natural scenes if the display is capable of creating very brightnon-color-saturated colors and darker highly saturated colors. The '574application further notes that a conventional RGB stripe display is acolor additive system whose non-saturated color brightness is limited tothe addition of partially-saturated colors. The brightness/saturationcolor gamut of the RGB system generally has brighter non-saturatedcolors, but fails to reproduce the very bright non-saturated colors.There is a trade-off between the brightness of the non-saturated colorsand the color saturation gamut of the filtered backlight display. Themore saturated the color filters, the less these filtered colors may addto the non-saturated brightness. This creates a luminance/saturationcompression in which the non-saturated colors are reduced in brightnessand saturated colors are compressed, desaturated, to fit within thelimitations of the compromise system.

The '574 application proposes several variations of display panelscomprising subpixels having more than three primary colors, referred toas “multiprimary” displays. In particular, the '574 application proposesvariations of a display panel having red. green and blue (RGB) primariesplus an additional non-saturated neutral colored subpixel which isconsidered to be a primary color. The non-saturated neutral coloredprimary subpixel is formed by an appropriate color filter. The neutralprimary color may be white, in which case the subpixel is formed using atransparent filter that allows substantially all of the light through,while the other three colors are formed by filtering out all but anarrow band of the spectrum. The white subpixel may have up to four ormore times the brightness of the colored subpixels. Thus, the use of awhite subpixel significantly increases the brightness of the panel whendisplaying non-saturated colors. When one fourth of the area of thedisplay panel is used for the white subpixel, the brightnesses of theremaining RGB subpixels are reduced by one fourth. However,non-saturated colors may be formed with a contribution from the brightwhite subpixel, giving significantly higher brightness. The resultingdisplay panel has a brightness/color gamut envelope shape that is closerto that of the ‘real world’.

FIG. 22 illustrates a portion 2230 of a display panel introduced in the'574 application as one embodiment of an RGBW display panel. Portion2230 of the display panel substantially comprises subpixel repeatinggroup 2200. In this embodiment, the subpixels are of substantially equalsize to maintain white balance. Subpixel repeating group 2200 iscomprised of 2 rows of 4 subpixels having the colors RBGW in the firstrow and GWRB in the second row. The number of colors in each row(R,G,B,W), is the same within a subpixel repeating group, resulting inbalanced white with existing backlights. As noted in the '574application, the horizontal and vertical resolution of a display panelsubstantially comprising subpixel repeating group 2200 should be thesame as panels with the conventional RGB stripe subpixel repeatinggroup, but the number of column drivers and thin-film transistors (TFTs)is reduced by one-third (⅓). Brightness gain depends on color filtertransmission; assuming 25% transmission (typical) for colored filtersand 100% for white, then transmission for white screen is(¾)*25+(¼)*100= 175/4=43.75% which is roughly a gain of 43.75/25=1.75.Note that a display panel is said to “substantially” comprise aparticular subpixel repeating group to allow for manufacturingconstraints: the subpixel repeating group array is repeated across apanel to complete a device with a desired matrix resolution, butsubpixel repeating groups occurring at the edges of a panel may not becomplete.

FIG. 23 illustrates another embodiment of an RGBW subpixel repeatinggroup. Portion 2330 of the display panel illustrated substantiallycomprises subpixel repeating group 2300 with its subpixels in a 1:2aspect ratio. Subpixel repeating group 2300 is also comprised of 2 rowsof 4 subpixels having the colors RBGW in the first row and GWRB in thesecond row. This layout may have fewer edge boundaries that give rise toliquid crystal disinclinations, and thus may have a higher contrast thanan LCD display panel with the conventional RGB stripe layout. A displaypanel substantially comprising subpixel repeating group 2300 has 25%white area; thus, it can have approximately 75% to 100% higherbrightness than the conventional RGB stripe panel with the sameresolution. Note that each color is on a square grid at 45°, asillustrated by diamond shaped dashed outline 2340 having green subpixel106 at each vertex of the diamond shape. This layout requires only onerow of subpixels to draw a single white line, while it still requirestwo subpixel columns.

FIG. 24 illustrates another embodiment of an RGBW subpixel repeatinggroup. Portion 2430 of the illustrated display panel substantiallycomprises subpixel repeating group 2400 comprising the same subpixelorder as subpixel repeating group 2300 of FIG. 23, but with itssubpixels in a one-to-three (1:3) aspect ratio, which may allow foreasier utilization of existing backplanes for this layout. A displaypanel substantially comprising subpixel repeating group 2400 would thenhave a higher MTFL in the horizontal axis than the conventional RGB itreplaces. It would also be approximately 75% brighter. The additionalhorizontal resolution may further reduce moiré distortion. If the inputsignal has higher resolution, such as scaling down a 1080i signal to a720 p HDTV LCD, or 720 p on a 480i TV, this panel may show up to 50%higher horizontal resolution than a conventional RGB stripe panel, thusshowing the full horizontal resolution of the higher resolution format.

As noted above, LCD contrast is set by many parameters, including lightleakage from disclinations or other LC distortions around the edges ofsubpixels. To cancel the light coming from these regions, the blackmatrix may be enlarged to cover this region. This may reduce lighttransmission, but also may improve contrast. FIG. 25 shows oneembodiment of a portion of an LCD panel with an enlarged black matrixadjacent to colored filter 2502; the enlarged black matrix tends to hidethe disinclination regions 2506 below.

The '574 application notes that, while the display panels describedtherein are suitable to LCD displays, the panels would find equalapplication in the area of incandescent lamp based displays, LightEmitting Diode (both organic and inorganic) based displays, Plasmadisplay panels (PDP) and many other various display technologies. The'574 application further notes that different aspect ratios and colorsubpixel order are also contemplated as being possible as alternativeembodiments of the RGBW display panels.

Co-pending and co-owned U.S. patent application Ser. No. 10/821,388 (the'388 application), entitled “Subpixel Rendering Filters for HighBrightness Displays” discloses techniques for rendering an input imagedata stream onto a display panel comprising one of the subpixelrepeating groups described in conjunction with FIGS. 22, 23 and 24. U.S.patent application Ser. No. 10/821,388 is published as U.S.2005/0225563, which is hereby incorporated by reference herein.

Images displayed on display panels comprising subpixel repeating group2300 (FIG. 23), for example, in which blue subpixel 102 is adjacent towhite subpixel 108 in the subpixel repeating group, may have certainvisual artifacts that are caused by the proximity of low luminance bluesubpixel 102 to high luminance white subpixel 108, and the lowerluminance red subpixel 104 to the relatively higher luminance greensubpixel 106. For example, such images may appear to have a “windowscreen” effect with low spatial frequency light and dark regions.

Image quality may be improved on such displays by employing the “split”subpixel technique disclosed above in the discussion of FIG. 1. FIG. 26illustrates subpixel repeating group 2300 from FIG. 23. Dividing, orsplitting, each of the blue subpixels 102 and white subpixels 108results in subpixel repeating group 2610. Treating red subpixels 104 andgreen subpixels 106 in the same manner produces subpixel repeating group2620. FIG. 27 shows a portion 2700 of a display panel comprising eight(8) instances of subpixel repeating group 2620. The split subpixels formcolumns of red and blue subpixels 2701, green and white subpixels 2702,blue and red subpixels 2703 and white and green subpixels 2704.

FIG. 28 is a diagram of an embodiment of a driver configuration 2800 forthe portion 2700 of a display panel comprising subpixel repeating group2620. Driver configuration 2800 utilizes the “tied” column driverconfiguration of FIG. 8B to reduce the number of column drivers neededto implement a display panel comprising subpixel repeating group 2610.In configuration 2800, the column drivers are denoted at the top of thefigure by inverted triangles. Column driver 2841, which drives firstcolumn 2701 of red and blue subpixels in the display portion of FIG. 27,also drives second column 2701 of red and blue subpixels via a second,crossover column line 2844; that is column driver 2841 sends signalsalong column line 2842, and along column line 2844. In a similar manner,the next column driver connected to column line 2846, which drives firstcolumn 2702 of green and white subpixels, also drives second column 2702of green and white subpixels via column line 2848. The split blue andwhite subpixels utilize a similar driver configuration: the columndriver connected to column line 2850 drives first column 2703 of blueand red subpixels and also drives second column 2704 of blue and redsubpixels via crossover column line 2852; the column driver connected tocolumn line 2854, which drives first column 2704 of white and greensubpixels, also drives second column 2704 of white and green subpixelsvia second column line 2856. Thus, a display device configured in thismanner includes a plurality of column drivers for sending signals to thesub-pixels to produce luminance values. The column drivers areconfigured such that a column driver providing a signal via a columnline to a first occurrence of a sub-pixel having a first one of theprimary colors includes a crossover column line connected to a secondoccurrence of the sub-pixel having the first one of the primary colors.

As noted above with respect to the discussion of FIG. 8A, the driverconfiguration could also be implemented as a one-to-one correspondenceof column drivers to columns in the display. The examples of thepolarity inversion schemes discussed above are applicable to the displayconfiguration shown in FIG. 27. Several co-pending and co-ownedapplications discuss additional considerations with regard to assigningpolarity schemes to display panels comprising subpixel repeating groupshaving an even number of subpixels. See, for example, U.S. PatentApplication Publications 2004/0246213, 2004/0246381, 2004/0246279,2004/0246393 and 2004/0246404, which are all hereby incorporated byreference herein.

FIG. 30 is a schematic diagram of a small portion 3000 of an enlargedTFT array of a display device having a display panel comprising subpixelrepeating group 2620, or a variation thereof FIG. 30 illustrates animplementation of the display panel in which the crossover connectionsbetween the same-colored split subpixels in a row are made inside theTFT array, thus eliminating half of the TFT's and the crossover columnlines shown in FIG. 28. A partial first row 3010 of subpixels having theconfiguration shown in FIGS. 26 and 27 includes red subpixel area 3012,green subpixel area 3014, blue subpixel area 3016 and white subpixelarea 3020 each having a TFT 3002. Subpixel color assignments are shownin the figure for convenience. The second occurrence (i.e., the secondhalf of the split subpixel) of each red, green, blue and white subpixelarea is connected by a crossover connection 3034 to the same-coloredsubpixel area that is configured with TFT 3002 such that TFT 3002 drivesboth same colored subpixel areas. This embodiment of TFT array 3000eliminates the TFTs for each connected same-colored subpixel in eachrow. This embodiment further eliminates column lines for the columnsthat include the second half of the same colored split subpixel.

FIG. 29 illustrates a display device comprising source image datareceiving unit which is configures to receive input image dataindicating an image for rendering on a display panel 2930 substantiallycomprising subpixel repeating group 2620. Display device also comprisessubpixel rendering unit 2920 which produces luminance values for eachsubpixel on panel 2930 according to techniques described herein and inrelated applications, to produce an output image on panel 2930.

While the display panels, subpixel rendering techniques and driverconfigurations have been described with reference to exemplaryembodiments, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the invention. Inaddition, many modifications may be made to adapt a particular situationor material to the teachings without departing from the essential scopethereof For example, alternative embodiments of the multiprimary displaypanels having different primary colors, different aspect ratios anddifferent color subpixel order are also contemplated as using the splitsubpixel technique disclosed above to improve image quality. Inaddition, some of the embodiments above may be implemented in otherdisplay technologies such as Organic Light Emitting Diode (OLED),ElectroLumenscent (EL), Electrophoretic, Active Matrix Liquid CrystalDisplay (AMLCD), Passive Matrix Liquid Crystal display (AMLCD),Incandescent, solid state Light Emitting Diode (LED), Plasma DisplayPanel (PDP), and Iridescent. Therefore, it is intended that theinvention not be limited to the particular embodiment disclosed as thebest mode contemplated for carrying out this invention, but that theinvention will include all embodiments falling within the scope of theappended claims.

1. A display device comprising a display panel comprising a plurality ofa sub-pixel repeating group; said sub-pixel repeating group comprisingsixteen sub-pixels; each sub-pixel having one of at least four primarycolors, wherein one of the primary colors is a non-saturated, neutralcolor; a source image data receiving unit configured to receive sourceimage data indicating an image, for rendering on said display panel; anda sub-pixel rendering unit configured to compute luminance values foreach subpixel of said display panel using the source image data.
 2. Thedisplay device of claim 1 wherein each sub-pixel that is not sub-pixelhaving a non-saturated neutral color is one of a red color sub-pixel, agreen color sub-pixel and a blue color sub-pixel.
 3. The display ofclaim 1 wherein said non-saturated neutral color is white.
 4. Thedisplay of claim 1 wherein said sub-pixel rendering unit uses an impliedsample area of the input image and locations of said sub-pixels on saiddisplay panel to determine a resample area from which to compute saidluminance values.
 5. The display of claim 1 wherein said display panelfurther includes a plurality of column drivers for sending signals tosaid sub-pixels to produce said luminance values; said column driversbeing configured such that a column driver providing a signal via acolumn line to a first occurrence of a sub-pixel having a first one ofthe primary colors includes a crossover column line connected to asecond occurrence of the sub-pixel having the first one of the primarycolors.